EP0324534B1 - Verfahren für die Herstellung eines keramischen Supraleiterkörpers - Google Patents

Verfahren für die Herstellung eines keramischen Supraleiterkörpers Download PDF

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EP0324534B1
EP0324534B1 EP89300020A EP89300020A EP0324534B1 EP 0324534 B1 EP0324534 B1 EP 0324534B1 EP 89300020 A EP89300020 A EP 89300020A EP 89300020 A EP89300020 A EP 89300020A EP 0324534 B1 EP0324534 B1 EP 0324534B1
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Prior art keywords
melt
substrate
temperature
oxygen
superconductive
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EP0324534A1 (de
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Ho Sou Chen
George Sanford Indig
Lionel Cooper Kimerling
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AT&T Corp
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American Telephone and Telegraph Co Inc
AT&T Corp
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/01—Manufacture or treatment
    • H10N60/0268—Manufacture or treatment of devices comprising copper oxide
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B37/00—Joining burned ceramic articles with other burned ceramic articles or other articles by heating
    • C04B37/003—Joining burned ceramic articles with other burned ceramic articles or other articles by heating by means of an interlayer consisting of a combination of materials selected from glass, or ceramic material with metals, metal oxides or metal salts
    • C04B37/005—Joining burned ceramic articles with other burned ceramic articles or other articles by heating by means of an interlayer consisting of a combination of materials selected from glass, or ceramic material with metals, metal oxides or metal salts consisting of glass or ceramic material
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/45—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides
    • C04B35/4504—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on copper oxide or solid solutions thereof with other oxides containing rare earth oxides
    • C04B35/4508—Type 1-2-3
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/653—Processes involving a melting step
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
    • C04B2237/02—Aspects relating to interlayers, e.g. used to join ceramic articles with other articles by heating
    • C04B2237/04—Ceramic interlayers
    • C04B2237/06—Oxidic interlayers
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2237/00—Aspects relating to ceramic laminates or to joining of ceramic articles with other articles by heating
    • C04B2237/30—Composition of layers of ceramic laminates or of ceramic or metallic articles to be joined by heating, e.g. Si substrates
    • C04B2237/32—Ceramic
    • C04B2237/34—Oxidic
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
    • Y10S117/906—Special atmosphere other than vacuum or inert
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S505/00—Superconductor technology: apparatus, material, process
    • Y10S505/725—Process of making or treating high tc, above 30 k, superconducting shaped material, article, or device
    • Y10S505/736—From free metal precursors

Definitions

  • This invention pertains to methods of producing a body (including a thin body such as a film on a substrate) from a melt, and to articles comprising a body produced by such a method.
  • the body is a superconductive oxide body.
  • compositions in the Y-Ba-Cu-O system can have superconductive transition temperatures T c above 77K, the boiling temperature of liquid N2 (see, for instance, M. K. Wu et al, Physical Review Letters , Vol. 58, March 2, 1987, page 908; and P. H. Hor et al, ibid, page 911).
  • Liquid nitrogen is generally considered to be one of the most advantageous cryogenic refrigerants, and attainment of superconductivity at or above liquid nitrogen temperature was a long-sought goal which until very recently appeared almost unreachable.
  • Thin films are formed by deposition of material on a substrate (e.g., by sputtering, evaporation, or decomposition of a solution), followed by a heat treatment that produces the appropriate crystal structure and composition (typically by adjustment of the oxygen content).
  • bulk bodies and thick films are generally produced by synthesizing a powder of the appropriate composition (e.g., YBa2Cu3O x ,x ⁇ 7), forming the powder into the desired shape (e.g., by hot pressing, drawing, extrusion, or silk screening of a slurry), and heat treating the resulting body such that sintering occurs, and such that the sintered material has the appropriate crystal structure and composition.
  • a further method which comprises melting of the oxide powder and forming bulk bodies by solidification of the oxide melt is discussed below.
  • the critical temperature T c i.e., the temperature at which a given body becomes superconductive, is an important parameter of a superconductor. Another important parameter is the maximum current density that can be supported by a body in the superconductive state. This "critical current density" J c decreases with both increasing temperature and increasing magnetic field.
  • Bulk bodies produced by this technique can have substantially larger J c than has been reported for sintered bodies of the same composition, and, significantly, J c can decrease more slowly with increasing magnetic field than has been reported for sintered bodies. These improvements are thought to be due at least in part to improved intergranular contact and/or to the presence of orientational correlation between neighboring crystallites. However, even though the melting technique of Jin et al results in substantially improved J c , the observed behavior still suggests that J c is limited at least to some extent by weak links, possibly associated with compositional inhomogeneity.
  • the Ba-cuprate system herein is the class of nominal general formula (M 1-x M x ) 1+y Ba 2-y Cu3O 9- ⁇ , where M and M' are chosen from Y, Eu, Nd, Sm, Gd, Dy, Ho, Er, Tm, Yb, Lu, La, Sc, Sr or combinations thereof, with typically 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, and 1 ⁇ ⁇ ⁇ 3.
  • M and M' are chosen from Y, Eu, Nd, Sm, Gd, Dy, Ho, Er, Tm, Yb, Lu, La, Sc, Sr or combinations thereof, with typically 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, and 1 ⁇ ⁇ ⁇ 3.
  • the material is frequently referred to as a "1-2-3-type" material.
  • the optimal oxygen content frequently corresponds to ⁇ ⁇ 2.
  • the La-cuprate system herein is the class of oxides of nominal general formula La 2-x M x CuO 4- ⁇ , where M is one or more divalent metals (e.g., Ba, Sr, Ca), and x ⁇ 0.05, and 0 ⁇ ⁇ ⁇ 0.5. Both Ba-cuprates and La-cuprates are generally considered to be ceramic materials.
  • crystal structure associated with superconductivity in the oxide is intended to include a high-temperature precursor phase of the superconductive phase, if such a precursor phase exists.
  • precursor phase in the well-known 1-2-3 compound YBa2Cu3O7 the precursor phase has tetragonal crystal structure and the superconductive phase has orthorhombic structure, with the transition temperature being in the approximate range 500°C-650°C, depending on the oxygen pressure.
  • the tetragonal phase has a crystal structure that is associated with superconductivity in the oxide.
  • a “superconductive body” herein is a body (including a layer on a substrate) which comprises a sufficient amount of superconductive material such that, at some temperature below the critical temperature, a d.c. electrical current can flow through at least part of the body without resistance.
  • the inventive process comprises forming a melt (the precursor melt) that comprises all but one of the chemical elements that make up the compound to be formed (the first compound), introducing the missing element (in the general case to be designated by the letter G) into at least a portion of the precursor melt such that the concentration of G in the portion of the melt reaches a critical concentration and consequently a quantity of the first compound is formed from the portion of the melt.
  • the introduction of G into the precursor melt typically is by exposure of the molten material to a G-containing atmosphere, e.g., to an oxygen or nitrogen atmosphere, or to a mixture of an inert gas such as He and G.
  • the temperature at which the first compound is formed typically is the same or higher than the temperature T of the precursor melt. This differs fundamentally from conventional solidification which involves a lowering of the melt temperature.
  • critical concentration is that concentration of G in the melt at which, at the temperature T and taking into account the existing nucleation conditions, the first compound is nucleated in the portion of the melt and is stable with respect to the melt, whereas all other compounds that could be formed from the portion of the melt do not form or their nucleation is relatively unstable with respect to the melt.
  • the portion of the precursor melt can comprise, prior to the above referred to introduction of G, a sub-critical concentration of G.
  • the precursor melt may contain one or more chemical elements (X) that are not constituents of the first compound.
  • Such an element may be present in the melt to, for instance, improve the solubility properties of the melt, or to improve the mechanical, thermal, electrical or other properties of the material formed by the inventive process.
  • more than one element i.e., G, G', . . .
  • the element G can be transferred through a massive melt to a substrate/melt interface, provided the concentration of G in the melt is tightly controlled.
  • the precursor melt typically is an elemental melt, i.e., formed from a charge that contains at least one of the constituents of the first compound in elemental form. Frequently all of the constituents are present in elemental form, but at least in some cases it may be desirable if one or more of the constituents is added as a compound. For instance, addition of a relatively insoluble constituent to the melt in the form of an oxide may improve the solubility properties of the melt.
  • the melt may be stoichiometric, i.e., contain the relevant elements in the ratio in which theses elements are found in the first compound, this is not necessarily so. Indeed, in some promising embodiments the melt is non-stoichiometric, as will be discussed in more detail below.
  • the melt is compositionally essentially homogeneous.
  • essentially homogeneous we mean that the melt may comprise zones of phase separation that have dimensions of the order of about 10 atomic diameters or less. Homogeneous melts result if the constituents of the melt are miscible at the temperature T. If the constituents are not miscible then mechanical means (e.g., ultrasonic agitation) may be able to produce an essentially homogeneous melt.
  • a melt will be considered to be homogeneous despite the presence of a thin boundary layer adjacent to a melt/substrate interface, where the boundary layer composition may differ from that of the bulk melt.
  • Other possible expedients for producing a homogeneous melt are the use of a relatively high melt temperature, addition of one or more "homogenizer” elements, or introduction of one or more of the constituents of the melt in the form of an appropriate compound.
  • the temperature T is selected such that T m ⁇ T ⁇ T o , where T m is the freezing temperature of the precursor melt, and T o is the melting temperature of the first compound. It will be understood that T need not be uniform throughout the portion of the melt but, for instance, can have a gradient imposed by external conditions or due to exothermic growth of the first compound.
  • the solidified first compound can be subjected to any desired treatment in the solid state. For instance, the first compound can be heat treated in a G-containing atmosphere to adjust the concentration of G in the material and/or to produce a desired crystal structure.
  • material other than the first compound will also be formed.
  • this may be the case if the composition of the melt, or of the portion of the melt, differs significantly from the composition of the first compound.
  • at least a significant fraction of the solid material formed by means of the inventive process will be first compound material.
  • the first compound material is formed on a substrate, and the other material (if present) overlies the first compound material.
  • Nucleation of the first compound is considered to be a significant aspect of the invention. Whereas nucleation does not necessarily require that the portion of the melt is in contact with a substrate, in many embodiments of the invention this will be the case.
  • a variety of materials can serve as substrates, including single crystal and polycrystalline metal oxides, semiconductors, and metals.
  • the inventive technique makes possible the use of substrate materials that could not be used in conjunction with prior art techniques, due to undesirable substrate/first compound interaction.
  • Some embodiments of the inventive process permit continuous formation of first compound material, e.g., the continuous formation of high T c superconductive material on a substrate such as a copper or silver wire.
  • the molten material consists substantially of molten metal (the melt contains one or more metallic elements M, M', ..., and the presence of minor amounts one or more non-metallic elements is not excluded), and G is oxygen, such that the first compound substantially is a metal oxide.
  • the oxide is a high T c superconductive oxide (e.g., Ba-cuprate or La-cuprate), and, for the sake of concreteness, the discussion from hereon will be primarily in terms of this preferred embodiment. No limitation of the invention to superconductive oxides is thereby implied.
  • other (i.e., non-superconductive) ceramics can be produced by means of the inventive method. Such ceramics may, for instance, be used as dielectric in capacitors.
  • Exemplary of non-oxidic materials that can be produced by the inventive method are nit:rides such as A1N.
  • high T c superconductive oxide bodies can be produced by an embodiment of the inventive process that comprises melting of the cationic constituents (e.g., Yb, Ba, and Cu) of the intended oxide such that a compositionally homogeneous (or essentially homogeneous) melt results, and that further comprises contacting all or a portion of the melt with oxygen such that the desired first compound is formed from the oxygenated melt, substantially without a drop in the temperature of the melt.
  • the atomic ratio of the metal elements is frequently the same in the melt as it is in the first compound. However, this is not necessarily so, and the melt composition in at least some cases can differ substantially from that of the first compound.
  • This unexpected feature of the inventive process indicates that under the conditions of the process, and in at least some materials systems, formation of one compound is strongly favored over that of other possible compounds.
  • This favored compound is the first compound. For instance, we have found that the formation of the compound YbBa2Cu3O x (x ⁇ 7) is favored over that of other (Yb, Ba, Cu)-oxides such as Yb2BaCuO y (y ⁇ 5) over a wide range of compositions.
  • superconductive Ba-cuprates such as YBa2Cu3O7 are favored over the corresponding non-superconductive compounds, provided all the cationic constituents of a given superconductive cuprate are present in the melt in concentrations that assure their statistical availability at the nucleation site.
  • the ability to form a given first compound from a non-stoichiometric melt has considerable practical significance. For instance, it makes possible the use of the method in cases where an essentially homogeneous stoichiometric melt cannot be formed, but where an essentially homogeneous melt containing all the relevant elements can be formed at some other ratio of the constituent elements. For instance, Y, Ba, and Cu in the ratio 1:2:3 do not form a homogeneous melt at a useful temperature but can do so if the copper content is substantially higher.
  • the melt may contain one (or possibly more) further element (e.g., Ag, Au, or Cd) that does not interfere with the formation of the desired compound and whose presence may improve certain properties of a body formed from the melt.
  • the presence of Ag in 1-2-3-type material may result in improved electrical and thermal stability of a superconductive body formed from the material. It is also contemplated that the presence of such a constituent may result, at least in some cases, in improved processing, as will be discussed in more detail below.
  • Solidification of the superconductive oxide typically is initiated at a predetermined location in the melt (e.g., at the interface between the melt and a solid substrate), and proceeds such that at least a substantial portion of the solidified material has the composition and crystal structure that is associated with superconductivity.
  • the oxygen content of the as-solidified material may, but need not, correspond to the optimal oxygen content of the superconductive material. If the initial oxygen content of the solidified material does not correspond to the desired oxygen content then an adjustment can be brought about during a later heat treatment, typically at a lower temperature in an O2-containing atmosphere. Typically an oxygen pressure of at least about 0.01 atmospheres is required to avoid decomposition of a superconductive oxide such as a barium cuprate.
  • the initial melt may be essentially oxygen-free or may contain some oxygen, provided the oxygen concentration is below the critical concentration at which, at the temperature of the melt, solidification occurs. Since the formation of the oxide frequently involves an exothermic reaction the initial temperature of the solidified material may be higher than that of the melt.
  • the temperature T of the melt is chosen such that T m ⁇ T ⁇ T o .
  • the temperature typically is also chosen with a view towards maintaining a stable melt composition and towards minimizing the interaction of the melt with the substrate. For instance, if one of the metallic elements has a relatively high vapor pressure (as does, for instance, Ba) it may be advantageous to choose a relatively low melt temperature. However, other considerations, e.g., melt miscibility, may require the choice of a relatively high melt temperature. Those skilled in the art will generally be able to determine an appropriate melt temperature with, at most, a minor amount of experimentation.
  • the invention is the possibility of producing superconductive oxide bodies of improved compositional homogeneity, as compared to bodies produced by prior art techniques.
  • metal constituents distributed essentially uniformly in superconductive metal oxide material produced according the invention (reflecting the essentially uniform distribution of the constituents of the homogeneous melt and, at least in the case of a stoichiometric melt, the absence of any thermodynamic driving force towards phase separation during solidification; the former is a distinguishing aspect with regard to the sintering method, and the latter with regard to the prior art melting technique), but so is the solidification-inducing element, e.g., oxygen.
  • the improved homogeneity is thought to be primarily due to the fact that a single, well-defined reaction product of the reaction of oxygen (or other solidification-inducing element) with the melt can be formed.
  • a contributing possibility is the relatively rapid diffusion of oxygen in the melt, and the much slower diffusion of oxygen in the solidified material. Since the relatively low J c of prior art superconductive bodies is generally ascribed to the presence of weak links which, in turn, are thought to be related to the existence of compositional inhomogeneities, the ability to produce material of improved compositional homogeneity is considered to be a significant aspect of the invention.
  • the inventive method has other advantageous features. For instance, it is typically a one-step procedure (production of the precursor material requires only melting of the metals) whereas prior art sintering techniques require repeated calcining and comminuting of the starting material. As compared to the prior art melt technique, it is believed that melt confinement is significantly less difficult in the inventive method, since the melt in the latter method is typically at a substantially lower temperature than in the former, and since molten metal typically is less reactive with refractory materials of the type likely to be used to confine the melt than is molten oxide.
  • the inventive method is also well adapted to the coating of a substrate (including a non-planar substrate such as a wire) with a layer of superconductive material, and even to carrying out such coating in a continuous manner.
  • the inventive process can be carried out at a relatively low temperature (e.g., melt temperature of about 900°C for YbBa2Cu3O7) and frequently does not require maintenance of the melt and/or solid oxide material in contact with the substrate at or close to the solidification temperature for any extended period of time, it is considered likely that substrate materials which poison the superconductive oxide thereon when used in prior art methods may be acceptable substrates for the practice of the inventive process.
  • a sintered Al2O3 substrate has been found to be an acceptable substrate for purposes of the inventive process but is generally considered unsuitable for use in prior art processes.
  • Ag and Au and, possibly, other metals such as the refractory metals and even Cu are also expected to be useful substrate materials and/or barrier layers when used in the inventive process.
  • the melt be essentially compositionally homogeneous. Typically this implies that the metal constituents are miscible.
  • mechanical mixing schemes may be devised which also can produce essentially homogeneous melts. Not all of the metals of interest with regard to high T c superconductors are miscible in the melt. For instance, Y, Ba, and Cu (ratio 1:2:3) do not form a homogeneous melt at 900°C, whereas in the same ratio and at the same temperature Yb, Ba, and Cu (or Eu, Ba, and Cu) do.
  • the addition of one or more further elements can result in a homogeneous melt.
  • the homogenizer can result in a homogeneous melt.
  • YBa2Cu3 does not form a homogeneous melt at temperatures of interest herein
  • Y x (Yb and/or Eu) 1-x Ba2Cu3 is expected to be miscible at such temperatures for some range of x . Partial substitution of Sr for Ba may also result in improved homogeneity.
  • Ag or Cu is expected to be a suitable homogenizer for, e.g., Ba-cuprates such as YBa2Cu3O7.
  • melt which is inhomogeneous at a relatively low temperature may be homogeneous at a higher temperature.
  • choice of melt temperature may at least in some cases be a significant aspect of the invention.
  • homogenization by mechanical or other appropriate means of a melt that exhibits some immiscibility may produce a melt that is useful in the practice of the invention. Exemplarily, this requires that the zones of phase separation be at most of the order of about 10 atomic diameters.
  • a desirable aspect of the inventive method is a relatively short oxygenation time.
  • it may frequently be advantageous to form a relatively thin melt layer on a substrate e.g., by dipping of a substrate into the melt, or by spinning of the melt onto a substrate.
  • the process such that the substrate temperature is at, or close to, the melt temperature when the melt is brought into contact with the substrate.
  • the substrate temperature is above T m , the freezing temperature of the melt.
  • the pressure typically should not be so high as to result in uncontrolled nucleation at the free surface of the melt, or in excessive heat evolution, since this typically would impede the oxygenation of the melt and/or cause inhomogeneity in the solidified material.
  • oxygen pressures in the range 0.1-5 atmospheres to be useful, but at least in some cases pressures outside of this range may also be useful.
  • Another aspect of the invention is associated with the nucleation of crystallites in the oxygenated melt.
  • Nucleation of the phase associated with superconductivity may at least in some cases be enhanced by provision of a substrate that is approximately lattice matched with the desired phase [e.g., (100) SrTiO3 is approximately matched with the basal plane of YbBa2Cu3O7].
  • lattice match is optional, and essentially single phase material can be obtained on non-lattice-matched substrates, e.g., single crystal MgO, and polycrystalline substrates, including sintered Al2O3.
  • the inventive method may not require the presence of a substrate.
  • a powder of the desired oxide may be formed by introducing droplets of the molten stoichiometric precursor material into an oxygen atmosphere, (e.g., droplets formed by an atomization process) and collecting the resulting particles. These particles can be used in substantially the same way as prior art powder, to produce superconductive bodies.
  • Solidification of the melt can be carried out in a variety of ways, with the particular choice typically depending on the nature of the body that is to be produced.
  • the melt can be spun or sprayed onto a substrate, a substrate can be dipped into the melt, the melt can be cast into a die or poured onto a rotating drum, or a substrate such as metal wire or tape can be pulled through the melt or otherwise brought into contact therewith (e.g., by dripping melt onto the moving substrate).
  • Single or multiple applications of liquid melt are possible with or without intervening oxidation. If a non-stoichiometric melt is used, then it may frequently be advantageous to remove the remaining liquid portion of a film formed on a substrate such that a substantially single phase deposit remains.
  • Such removal can, for instance, be by means of a blast of hot gas. It is also possible to apply the melt to a substrate, cause the temperature of the melt to drop below T m such that the melt solidifies, then reheat (e.g., by laser or electron beam heating) the solidified material such that at least a portion thereof melts, followed by exposure of the molten material to oxygen such that solidification of the desired oxide occurs.
  • reheat e.g., by laser or electron beam heating
  • Such a process would be advantageously employed to produce superconductive wires and the like and could also be used to, for instance, form a protective ceramic coating on parts such as turbine blades.
  • the substrate in addition to providing mechanical support (and, possibly, electrical and thermal stabilization) provides the nucleation site for the superconductive oxide.
  • the nucleation site can be provided in a variety of ways, and we contemplate all possible ways to initiate the formation of crystallites.
  • the interfaces of the melt with particles of a dispersed powder can constitute sites for nucleation. It is expected to even be possible to initiate nucleation at a liquid/gas interface (e.g., on the surface of a melt stream or droplet falling through an oxygen atmosphere). In general, it is believed that heterogeneous nucleation is preferable to homogeneous nucleation.
  • the solidified material After solidification of the superconductive oxide it is typically subjected to some further processing steps so as to obtain the desired shape and/or properties. For instance, it will frequently be found desirable to cool the solidified material in an oxygen-containing atmosphere to an appropriate intermediate temperature (e.g., about 500°C in the case of YbBa2Cu3O7) and maintain it at that temperature in the atmosphere, such that the oxygen content of the material is optimized and/or the transformation to the crystal phase that is associated with superconductivity can take place in a controlled manner. Furthermore, in some cases it may be desirable to subject the solidified material to a sintering treatment at a temperature close to the melting temperature of the material.
  • an appropriate intermediate temperature e.g., about 500°C in the case of YbBa2Cu3O7
  • the inventive method can be applied in a variety of ways. For instance, it can be used to form a superconductive film or layer on a substrate, including a non-planar substrate such as a wire or tube. Bodies can be produced in batch fashion or by a continuous method (both with or without seeding). Replenishment of the melt, to insure steady state conditions, will typically be required, as will be apparent to those skilled in the art. By repeated application of the technique bodies of substantial thickness could be produced. Furthermore, the method can be used to make a superconductive connection between two superconductive bodies by forming the molten metal layer connecting the two bodies that are to be joined together, and exposing the combination to oxygen. This latter embodiment of the invention provides, it is believed, the only currently known way to form a high T c bond between two high T c superconductor bodies.
  • FIG. 1 shows a photomicrograph of a layer of material (YbBa2Cu3O7) formed by the inventive process on an essentially lattice matched substrate [(100)-oriented SrTiO3].
  • the material is single phase, with essentially all of the material having epitaxial orientation, with the c-axis normal to the substrate.
  • FIG. 3 similarly shows a photomicrograph of a layer of the same composition, formed in essentially the same manner, except that the substrate [(100)MgO] is not lattice matched with the material.
  • the material is single phase, and has heavy texture, with the c-axis perpendicular to the substrate.
  • Superconductive bodies frequently comprise both superconductive material and normal (i.e., non-superconductive at temperatures of technological interest) metal, with the latter typically forming a cladding for the former.
  • the cladding not only provides mechanical support and serves to electrically and thermally stabilize the superconductor but also protects the superconductor from contact with harmful agents such as water.
  • FIG. 2 schematically depicts an exemplary body according to the invention, namely, a tape with a multiplicity of elongate superconductive bodies surrounded by normal metal cladding, wherein metal tapes 20, 21, and 22 serve as cladding for superconductive elements 23.
  • a tape can be produced by, for instance, casting the melt into the grooves in tape 20 and forming the oxide according to the invention, carrying out the analogous process with tape 21, optionally heat treating the two tapes to attain the desired crystal structure and oxygen content of the superconductor elements, then assembling tapes 20, 21, and 22 into a unitary structure by some appropriate known technique such as soldering or welding. Other techniques for forming such a structure will be apparent to those skilled in the art.
  • a layer of metal (analogous to 21) is formed on 20 by vapor deposition
  • grooves are formed in the layer by some appropriate process (e.g., photolithography and etching)
  • superconductive oxide bodies are formed in the grooves by the inventive technique
  • the ribbon is completed by vapor deposition of a covering layer analogous to 22.
  • inventive method is well suited for the manufacture of composite (superconductive/metal) structures by a continuous process.
  • it is well suited for the manufacture of elongate composite bodies such as superconductive wire and tape.
  • a wire can exemplarily be prepared by applying the melt to a Ag (or Ag-coated or bare Cu) wire, forming the oxide from the melt, heat treating the oxide in O2, and applying a layer of metal (e.g., Ag or Cd) over the oxide. If desired this process can be repeated so as to produce a wire in which annular superconductive layers alternate with annular normal metal layers.
  • a Ag or Ag-coated or bare Cu
  • a layer of metal e.g., Ag or Cd
  • Bodies produced according to the inventive method can be used in the same way as prior art superconductive bodies.
  • Representative of such use are magnets and transmission lines comprising superconductive wire or tape formed according to the invention.
  • a significant aspect of the invention takes advantage of the observation that solidified material as initially yielded by liquid of the source (also referred to as the melt) is of a composition determined on the basis of energetics. Stated differently, atomic ratio in the solidified material and independent of, e.g., oxygen may differ from the ratio of the same atoms in the liquid. This is of particular significance in the growth of solid material in which "stoichiometric" ratio of such atoms may not conveniently yield liquid source under temperatures and/or other conditions desired in the process.
  • a particular mechanistic explanation takes the form of a free energy minimum at the interface between the substrate and the described solid, and/or at the interface between the solid and the liquid source.
  • the aspect of the invention under discussion requires at least two "cations” in a liquid and of course an energetic preference for a yielded solid in which the ratio of those two “cations” differs.
  • this aspect of the invention is of course applicable with the liquid composition containing additional material.
  • Discussion elsewhere is directed to the use of such additional material serving as solvent e.g., silver.
  • the 10 atomic % requirement continues to apply to the ratio of "cations" - in this instance, e.g., ratio of perhaps M expressed as a percentage of the totality of M+M'+Cu.
  • Example 15 may be regarded as involving a liquid in which cations would be yielded to the solid from a liquid in which excess Cu serves as a solvent.
  • Solidification may simply be established (e.g., by removal of wetting liquid) or it may be continued to yield overlying solid which may serve in some capacity different from that of initial solid.
  • a non-superconducting overlying solid e.g., of lesser M content, may serve a chemical function (protective) or a mechanical function.
  • Continuous processing in which solidifying matter of the composition of the "initial solid" is continually replenished is contemplated.
  • prototypical superconductor e.g., YbBa2Cu3O x (x ⁇ 7)
  • a continuous substrate body e.g., a copper filament

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Claims (14)

  1. Verfahren zur Herstellung eines Gegenstandes, der eine Menge eines supraleitenden Oxidmaterials enthält, mit wenigstens zwei verschiedenen, einen Supraleiter bildenden metallischen Elementen M und M', Cu und Sauerstoff, jeweils in einem definierten Verhältnis x:x':y:z,
    wobei das Verfahren umfaßt:
    a) Bilden einer Schmelze aus einem Vorläufermaterial, das derart ausgewählt ist, daß wenigstens die zwei metallischen Elemente M und M' und Cu in der Schmelze anwesend sind, und
    b) Bewirken einer Verfestigung wenigstens eines Teils der Schmelze, wobei der Anteil des supraleitenden Oxidmaterials der verfestigte Teil der Schmelze ist oder von diesem abgeleitet wird,
    dadurch gekennzeichnet, daß
    c) das Vorläufermaterial wenigstens eines von den zwei Supraleiter bildenden metallischen Elementen und Cu in elementarer Form enthält,
    d) wenigstens der genannte Teil der Schmelze bei einer Temperatur T ist, mit Tm < T < T₀ , wobei Tm die Gefriertemperatur der Schmelze und T₀ eine zu dem supraleitenden Oxidmaterial gehörende Schmelztemperatur ist, und
    e) Schritt b) das In-Kontakt-Bringen wenigstens des genannten Teils der Schmelze mit einer Sauerstoff enthaltenden Atmosphäre derart umfaßt, daß die Konzentration des Sauerstoffs in dem Teil der Schmelze erhöht wird, so daß im wesentlichen ohne einen Abfall der Temperatur des Teils der Schmelze ein festes Oxid aus dem Teil der Schmelze gebildet wird, wobei das feste Oxid wenigstens die zwei Supraleiter bildenden metallischen Elemente, Cu und Sauerstoff, jeweils in einem Verhältnis x:x':y:z' enthält, wobei z' verschieden von z sein kann, dies aber nicht sein muß.
  2. Verfahren nach Anspruch 1,
    in welchem die Schmelze wenigstens zwei Supraleiter bildende, metallische Elemente und Cu in einem Verhältnis enthält, das von x:x':y abweicht.
  3. Verfahren nach einem der Ansprüche 1 und 2,
    in welchem vor dem Einwirkenlassen der Sauerstoff enthaltenden Atmosphäre die Schmelze im wesentlichen sauerstofffrei ist.
  4. Verfahren nach einem der Ansprüche 1 bis 3,
    umfassend eine Hitzebehandlung des festen Oxids bei einer Temperatur oder Temperaturen unterhalb der Temperatur T₀ in einer Sauerstoff enthaltenden Atmosphäre.
  5. Verfahren nach Anspruch 1,
    umfassend das In-Kontakt-Bringen eines Substrates mit dem genannten Teil der Schmelze, wobei das Substrat bei einer Temperatur ist, die im wesentlichen gleich der Temperatur T ist.
  6. Verfahren nach Anspruch 1,
    in welchem die Schmelze ferner wenigstens eines von Ag, Au und Cd enthält.
  7. Verfahren nach Anspruch 1,
    in welchem die zwei Supraleiter bildenden metallischen Elemente aus Ba, Y und den Seltenen Erden ausgewählt sind.
  8. Verfahren nach Anspruch 1,
    in welchem das supraleitende Oxid ein Y enthaltendes Ba-Cuprat enthält und die relative Konzentration an Y in der Schmelze wenigstens 10 % geringer als die relative Konzentration an Y in dem Ba-Cuprat ist.
  9. Verfahren nach Anspruch 8,
    in welchem das Y enthaltende Ba-Cuprat eine nominelle Zusammensetzung YBa₂Cu₃O₇ hat.
  10. Verfahren nach Anspruch 1,
    umfassend das In-Kontakt-Bringen eines Substrates mit dem genannten Teil der Schmelze, wobei das Substrat bei einer Temperatur oberhalb Tm ist, wobei wenigstens ein Anteil des Substrates im wesentlichen aus Kupfer besteht.
  11. Verfahren nach Anspruch 1,
    in welchem der Gegenstand einen vorexistierenden ersten und zweiten supraleitenden Oxidkörper enthält und das Verfahren das Bewirken des In-Kontakt-Tretens des genannten Teils der Schmelze sowohl mit dem ersten und dem zweiten supraleitenden Oxidkörper und das Ausführen von b) derart umfaßt, daß der verfestigte Anteil der Schmelze den ersten mit dem zweiten supraleitenden Oxidkörper verbindet.
  12. Verfahren nach Anspruch 1,
    in welchem b) das Bilden von Schmelztröpfchen und das In-Kontakt-Bringen der Tröpfchen mit Sauerstoff derart, daß die Tröpfchen in feste Oxidpartikel umgeformt werden, umfaßt.
  13. Verfahren nach einem der Ansprüche 1 bis 4 und 6 bis 9, in welchem das Verfahren das Ausbilden einer Schicht aus einem festen Material, das Kupfer und wenigstens die zwei Supraleiter bildenden metallischen Elemente M und M' enthält, umfaßt und Schritt b) das Erhitzen der Schicht aus festem Material derart, daß wenigstens ein Teil von diesem schmilzt, umfaßt.
  14. Verfahren nach Anspruch 13,
    dadurch gekennzeichnet, daß das Verfahren als kontinuierliches Verfahren durchgeführt wird.
EP89300020A 1988-01-11 1989-01-04 Verfahren für die Herstellung eines keramischen Supraleiterkörpers Expired - Lifetime EP0324534B1 (de)

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US5259885A (en) * 1991-04-03 1993-11-09 American Superconductor Corporation Process for making ceramic/metal and ceramic/ceramic laminates by oxidation of a metal precursor
GB9112109D0 (en) * 1991-06-05 1991-07-24 Cambridge Advanced Materials Melt-texturing of superconductors
US5786304A (en) * 1992-04-03 1998-07-28 Nippon Steel Corporation Joining product of oxide superconducting material and process for producing the same
JPH0782049A (ja) * 1993-09-17 1995-03-28 Kokusai Chodendo Sangyo Gijutsu Kenkyu Center Ｙ系酸化物超電導体の接合方法
US5872081A (en) * 1995-04-07 1999-02-16 General Atomics Compositions for melt processing high temperature superconductor
JP3183192B2 (ja) * 1996-10-02 2001-07-03 株式会社村田製作所 酸化物単結晶の製造方法および酸化物単結晶
GB2349382A (en) * 1999-04-27 2000-11-01 Secr Defence Ceramic materials; superconductors
JP4174332B2 (ja) * 2003-01-23 2008-10-29 財団法人国際超電導産業技術研究センター 酸化物超電導体の製造方法及び酸化物超電導体とその前駆体支持用基材
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DK9289A (da) 1989-07-12
AU2767889A (en) 1989-07-20
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ATE93655T1 (de) 1993-09-15
JPH0534293B2 (de) 1993-05-21
US5100870A (en) 1992-03-31

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